Suction or pressure valves for use in a reciprocating compressor are heretofore known which are constructed with a valve seat having concentrically arranged, ring-shaped fluid flow passages An example is an invention co-invented by George J. Safford, which is disclosed in European patent application No. 303828, published Feb. 22, 1989. This application shows a seat, a movable plastic valve plate, a flat spring and a guard. The seat has concentrically arranged, ring-shaped, fluid flow passages which are countersunk. The movable plate also has concentrically arranged, arcuate-shaped fluid flow passages which are offset relative to the circular countersunk fluid flow passages of the seat. The top surface of the valve plate has a plurality of arcuate projections extending vertically therefrom. The bottom surface of the plate is flat and has land areas which cover the seat passages and will sealingly engage the seat. The spring has a plurality of arcuate resilient spring fingers. The arcuate spring fingers are positioned to contact projections and normally bias the plate against the fluid passages to maintain a sealed relationship between the plate and seat to prevent fluid from passing through the seat passages. When the pressure becomes sufficiently great in the seat passages, the fluid acts against the plate and forces it outward against the spring. This opens both the seat and plate fluid flow passages to allow the fluid to pass through the valve. A guard is located on the outward side of the spring. The spring is between the plate and the guard. The guard has an annular side wall that contacts the seat. The guard acts as a stop for the plate and serves as a support for the spring. When the pressure decreases sufficiently, the spring fingers force the plate bottom surface against the seat passages and, once again, the plate is in a sealing relationship with the seat.
Other spring members heretofore known include a coiled spring as disclosed in U.S. Pat. Nos. 4,307,751 and 4,184,508, a curved spring plate as disclosed in U.S. Pat. No. 3,945,397 or a flat spring which also serves as the plate member as disclosed in U.S. Pat. No. 4,164,238.
A shortcoming of some prior art reciprocating compressor valves is that the plate lift is limited due to the cyclical impact on the guard by the plate which causes the plate to undergo fatigue and metal cracking. Attempts to solve this shortcoming have been to increase the area and strength of the sealing portions of the plate, but such a design decreases the fluid, i.e, air flow. In addition, the guard used with the prior art valves must have sufficient thickness to contain and fasten the coil springs. A thinner guard is desired, however, to allow for greater fluid flow.
A shortcoming of the prior art valve which uses the flat circular spring is that its diameter is restricted in size to, typically, greater than 5 inches. The arcuate spring fingers design pose the restriction because a reduced diameter for the fingers requires shorter spring fingers which, at high lift, causes higher strains leading to finger breakage. Alternatively, the finger length could be maintained the same, but the number of fingers would have to be reduced below values acceptable for preload.